Method of using a gas hood

Abstract

This invention discloses a method for configuring an air hood, wherein the air hood has an intake port, a constriction section, and an outlet. The intake port is connected to the front end of the constriction section, which is a rectangular cone that tapers from front to back, with a constriction angle on its long side. The outlet is connected to the rear end of the constriction section. The outlet is connected to a pipe, which in turn is connected to a fan, so that when a pollution source at the front end of the intake port emits gaseous pollutants, the gaseous pollutants are drawn in through the intake port and then discharged outward through the outlet. The method for configuring the air hood mainly includes the following steps: A. confirming the range of gaseous pollutants emitted by the pollution source, and B. selecting the angle of the constriction angle. In this way, gaseous pollutants can be effectively removed, and power consumption can be reduced to save energy and carbon.

Description

Technical Field

[0001] This invention relates to a method for using and configuring an air hood, and more particularly to a method for using and configuring an air hood that can effectively remove gaseous pollutants and reduce power consumption to save energy and carbon. Background Technology

[0002] A basic air hood typically consists of an intake (square, rectangular, round, or slotted) and an outlet, connected by a constriction section. The outlet is connected to a duct, which in turn connects to a fan. When a pollution source near the intake emits gaseous pollutants, the intake covers the dispersion area of ​​the pollutants. The fan's suction power is then increased to draw the pollutants in through the intake and expel them through the outlet.

[0003] In actual use, although the above structure can help to discharge gaseous pollutants, the airflow characteristics of different types of air hoods are quite different. Therefore, in cases of misuse of the air hood, the efficiency of discharging gaseous pollutants is often reduced, or the expected exhaust effect can only be achieved after a significant increase in power consumption. Summary of the Invention

[0004] In view of this, the main objective of the present invention is to provide a different method of using and configuring air hoods than existing ones, so as to improve the above-mentioned disadvantages.

[0005] One objective of this invention is to address the problem that existing air hoods are often misused in practical applications, resulting in reduced efficiency in emitting gaseous pollutants or increased power consumption. The invention provides a method for configuring an air hood that, based on empirical results in accordance with gas dynamics, utilizes air hood types with different contraction angles. This method not only effectively removes gaseous pollutants from pollution sources near the intake port but also reduces power consumption, thereby saving energy and carbon.

[0006] To achieve the above objectives, the present invention provides a method for configuring an air hood, the air hood having an intake port, a constriction section, and an outlet. The intake port is connected to the front end of the constriction section, which is a rectangular cone that tapers from front to back, with a constriction angle on its long side. The outlet is connected to the rear end of the constriction section. The outlet is connected to a pipe, which in turn is connected to a fan, so that when a pollution source at the front end of the intake port emits gaseous pollutants, the gaseous pollutants are drawn in through the intake port and then discharged outwards through the outlet. The above-mentioned method for configuring the air hood mainly includes the following steps: A. Confirming the range of gaseous pollutants emitted by the pollution source; and B. Selecting the angle of the constriction angle.

[0007] In practice, step A involves confirming the width of the gaseous pollutants emitted by the pollution source, which corresponds to the long side of the contraction section.

[0008] In practice, the length of the air inlet is L and the width of the air inlet is W. When L / W ≤ 5, it is called an opening hood. When the gaseous pollutants in step A are widely dispersed and a more uniform air inlet velocity is required, the contraction angle is ≤ 90° in step B. If the gaseous pollutants in step A are concentrated in a specific area and the air intake needs to be reduced, the contraction angle is > 90° in step B.

[0009] In practice, the length of the air inlet is L and the width of the air inlet is W. When L / W > 5, it is called a single-slot hood. When the gaseous pollutants in step A are widely dispersed and a more uniform air inlet velocity is required, the contraction angle is ≤60° in step B. If the gaseous pollutants in step A are concentrated and the air intake needs to be reduced, the contraction angle is >60° in step B.

[0010] To further understand the present invention, preferred embodiments are described below, along with drawings and reference numerals, to explain in detail the specific composition of the present invention and the effects it achieves. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the air hood structure of the present invention.

[0012] Figure 2 The flow field diagram of the Opening Hood (L / W = 1.54, α = 30°) of the present invention is shown on the front view elevation parallel to the long side at z = 0.

[0013] Figure 3 The flow field diagram of the Opening Hood (L / W = 1.54, α = 30°) of the present invention is shown in the side view elevation with x = 0 parallel to the short side.

[0014] Figure 4 The flow field diagram of the Opening Hood (L / W = 1.54, α = 30°) of the present invention is viewed from above at y = 0 (inlet) on a horizontal plane.

[0015] Figure 5 The flow field diagram of the Opening Hood (L / W = 1.54, α = 150°) of the present invention is shown on the front view elevation parallel to the long side at z = 0.

[0016] Figure 6 The flow field diagram of the Opening Hood (L / W = 1.54, α = 150°) of the present invention is shown in the side view elevation with x = 0 parallel to the short side.

[0017] Figure 7This is a top-view horizontal flow field diagram of the Opening Hood (L / W = 1.54, α = 150°) of the present invention at y = 0 (inlet).

[0018] Figure 8 This is a top-view flow field diagram of the Opening Hood (L / W = 1.54) of the present invention at y = 0 (inlet).

[0019] Figure 9 This is a top-view horizontal flow field diagram of the Slot Hood (L / W = 6.06) of the present invention at y = 0 (inlet).

[0020] Figure 10 This is a top-view horizontal flow field diagram of the Slot Hood (L / W = 10.00) of the present invention at y = 0 (inlet).

[0021] Figure 11 This is a flow field diagram of the frontal elevation of the low-velocity zone at the edge of the intake of the Opening Hood (L / W = 1.54, α = 30°) of the present invention.

[0022] Figure 12 This is a flow field diagram of the frontal elevation of the low-velocity zone at the edge of the intake of the Opening Hood (L / W = 1.54, α = 150°) of the present invention.

[0023] Figure 13 This is a dimensionless velocity distribution diagram of the Opening Hood (L / W = 1.54) of the present invention at different contraction angles α on the centerline.

[0024] Figure 14 The dimensionless velocity distribution diagrams of the Slot Hood (L / W = (a) 6.06, (b) 10.00) of the present invention at different contraction angles α on the centerline.

[0025] Figure 15 The dimensionless velocity u / u of the Opening Hood (L / W = 1.54) of the present invention at y / Dh = 0.10. ave Horizontal distribution diagram.

[0026] Figure 16 The Opening Hood (L / W = 1.54) of this invention is at a dimensionless velocity u / u = 0.50 at y / Dh = 0.50. ave Horizontal distribution diagram.

[0027] Figure 17The Slot Hood (L / W = 6.06) of the present invention has a dimensionless velocity u / u at y / Dh = 0.10. ave Horizontal distribution diagram.

[0028] Figure 18 The Slot Hood (L / W = 6.06) of the present invention is at a dimensionless velocity u / u at y / Dh = 0.50. ave Horizontal distribution diagram.

[0029] Figure 19 The Slot Hood (L / W = 10.00) of the present invention has a dimensionless velocity u / u at y / Dh = 0.10. ave Horizontal distribution diagram.

[0030] Figure 20 The Slot Hood (L / W = 10.00) of the present invention has a dimensionless velocity u / u at y / Dh = 0.50. ave Horizontal distribution diagram.

[0031] Figure 21 For the Opening Hood (L / W = 1.54) of this invention, when the contraction angle α changes, multiple dimensionless velocities u / u on the plane of symmetry parallel to the long side (y / Dh) are generated. ave The diagram shows the lateral distribution non-uniformity.

[0032] Figure 22 For the Slot Hood (L / W = 6.06) of this invention, when the contraction angle α changes, multiple dimensionless velocities u / u on the plane of symmetry parallel to the long side are generated. ave The diagram shows the lateral distribution non-uniformity.

[0033] Figure 23 For the Slot Hood (L / W = 10.00) of this invention, when the contraction angle α changes, multiple dimensionless velocities u / u on the plane of symmetry parallel to the long side are... ave The diagram shows the lateral distribution non-uniformity.

[0034] Figure 24 For this invention, at y / Dh = 0.10, the Opening Hood and Slot Hood have multiple dimensional velocities u / u on the planes of symmetry parallel to the long side and parallel to the short side, respectively. ave Graph showing the variation of lateral distribution non-uniformity η with contraction angle α.

[0035] Figure 25 This is a diagram showing the design parameters for the Slot Hood method B of the present invention.

[0036] Figure 26This is a velocity distribution diagram of several contraction angles α along the transverse central symmetry line of the air hood intake port using the Slot Hood method B of the present invention.

[0037] Figure 27 The figure shows that the lateral non-uniformity of the inlet velocity distribution increases with the increase of the contraction angle α in the Slot Hood method B of the present invention.

[0038] Figure 28 This is a diagram showing the design parameters for the distance between the leading edge of the suction port and the suction surface of the air hood in the Slot Hood method C1 of the present invention.

[0039] Figure 29 The minimum critical value Scri diagram for the distance between the leading edge of the suction port and the suction surface of the air hood in the Slot Hood method C1 of the present invention is suggested to be within the range of 3.5 ≤ Hhood < 5 cm.

[0040] Figure 30 The minimum critical value Scri diagram for the distance between the leading edge of the suction port and the suction surface of the air hood in the Slot Hood method C1 of the present invention is suggested to be used in the range of 5 ≤ Hhood < 10 cm.

[0041] Figure 31 The minimum critical value Scri diagram for the distance between the leading edge of the suction port and the suction surface of the air hood in the Slot Hood method C1 of the present invention is suggested to be used in the range of 10 ≤ Hhood < 15 cm.

[0042] Figure 32 The minimum critical value Scri diagram for the distance between the leading edge of the suction port and the suction surface of the air hood in the Slot Hood method C1 of the present invention is recommended to be within the range of 15cm≤Hhood.

[0043] Figure 33 This is a diagram showing the design parameters for the distance between the leading edge of the intake port and the side of the air hood in the Slot Hood method C2 of the present invention.

[0044] Figure 34 The minimum critical value Scri diagram for the distance between the leading edge of the intake port and the side of the air hood is shown in the Slot Hood method C2 of the present invention. It is recommended to use a range of 5 cm ≤ Hhood < 10 cm.

[0045] Figure 35 The minimum critical value Scri diagram for the distance between the leading edge of the intake port and the side of the air hood is shown in the Slot Hood method C2 of the present invention. It is recommended to use a range of 10cm ≤ Hhood.

[0046] Figure 36 This is a diagram showing the design parameters for the distance between the air intake and the lower plate of the air hood in the Slot Hood method C3 of the present invention.

[0047] Figure 37 The minimum critical value Hcri diagram for the distance between the leading edge of the intake port and the side of the air hood in the Slot Hood method C3 of the present invention is suggested to be used in the range of 1cm≤S < 6cm.

[0048] Figure 38 For the Slot Hood method C3 of the present invention, the minimum critical Hcri diagram of the distance between the leading edge of the intake port and the side of the air hood is recommended to be within the range of 6cm≤S.

[0049] Figure 39 This is a diagram showing the design parameters for the Multiple-Slot Hood method A of the present invention.

[0050] Figure 40 This is a velocity distribution diagram of several contraction angles α along the transverse central symmetry line of the air hood intake port using the Multiple Slot Hood method A of the present invention.

[0051] Figure 41 The figure shows that the lateral non-uniformity of the inlet velocity distribution increases with the increase of the contraction angle α when using the Multiple-Slot Hood method A of the present invention.

[0052] Figure 42 This is a diagram showing the geometric parameters used in designing the Multiple-Slot Hood of this invention.

[0053] Figure 43 This is a diagram showing the design parameters for the Multiple-Slot Hood method B of the present invention.

[0054] Figure 44 One of the suction ports of this invention is located in the Multiple-Slot Hood on the upper plate of the air hood cavity, and the uppermost suction slot has a dimensionless local inlet velocity u / u. ave A graph showing the variation of the dimensionless lateral distance ξ / L.

[0055] Figure 45 The Scri diagram shows the minimum critical value of the suction port in the Multiple-Slot Hood method B of the present invention. It is recommended to use a range of W ≤ 10 cm.

[0056] Figure 46 The minimum critical value Scri diagram for the intake hole in the Multiple-Slot Hood method B of the present invention is shown. It is recommended to use a range of 10 cm < W ≤ 17 cm.

[0057] Figure 47The minimum critical value Scri diagram for the intake hole in the Multiple-Slot Hood method B of the present invention is shown. The recommended range is 17 cm < W ≤ 32 cm.

[0058] Figure 48 The minimum critical value Scri diagram for the intake hole in the Multiple-Slot Hood method B of the present invention is shown. The recommended range is 32 cm < W ≤ 47 cm.

[0059] Figure 49 The minimum critical value Scri diagram for the intake hole in the Multiple-Slot Hood method B of the present invention is shown. The recommended range is 47 cm < W ≤ 55 cm.

[0060] Figure 50 The Scri diagram shows the minimum critical value of the suction port in the Multiple-Slot Hood method B of the present invention. It is recommended to use a range of 55 cm < W ≤ 70 cm.

[0061] Figure 51 The ACGIH Manual recommends a conventional air hood design with a required airflow volume Q. s With wind speed V s .

[0062] Explanation of reference numerals in the attached diagram: 1-Air hood; 2-Intake port; 3-Contraction section; 31-Long side; 32-Short side; α-Contraction angle; 4-Outlet; 5-Pipe; L-Length of intake port; W-Width of intake port; D-Diameter of outlet. Detailed Implementation

[0063] Figure 1In a preferred embodiment of the present invention, the air hood 1 mainly includes an intake port 2, a constriction section 3, and an outlet 4. The intake port 2 is connected to the front end of the constriction section 3. The constriction section 3 is a rectangular pyramid that gradually narrows from front to back, and has two parallel long sides 31 and two parallel short sides 32. The two long sides 31 of the constriction section 3 have the same constriction angle α. The outlet 4 is connected to the rear end of the constriction section 3, and the outlet 4 is connected to a pipe 5, which in turn is connected to a fan. When a pollution source at the front end of the intake port 2 emits gaseous pollutants, the gaseous pollutants are drawn in through the intake port 2 and then discharged outward through the outlet 4. Here, L and W represent the length and width of the intake port 2, respectively. The origin of the rectangular coordinate system is located at the center of the intake port. The arrow in the y-direction represents the front end of the air hood 1, and the opposite direction defines the rear end of the air hood 1. D is the diameter of the outlet. According to the American College of Industrial Hygiene Technicians (ACGIH) Manual, hoods with an L / W ratio ≤ 5 are classified as opening hoods, and those with an L / W ratio > 5 are classified as slot hoods. The configuration method for hood 1 mainly includes the following steps: A. Confirming the range of gaseous pollutants emitted from the pollution source, and B. Selecting the angle of contraction. In this way, hood types with different contraction angles can be used based on the emission patterns of different gaseous pollutants, effectively removing gaseous pollutants near the intake port 2 and reducing power consumption.

[0064] Characteristics of the air hood flow field: Regarding A. Flow field characteristics, Figures 2-4 Display the flow field of an opening hood with L / W = 1.54 and α = 30° on the front view (z = 0, parallel to the long side), the side view (x = 0, parallel to the short side), and the top view (y = 0, from the intake). The intake (length × width) = (L × W) = (1 m × 0.65 m), with an area A = 0.65 m². 2 The outlet diameter D = 0.10 m, and the contraction section length E = 1.679 m. The intake volume Qs = 117 cm⁻¹, the outlet velocity is 248 m / s, and the average intake velocity u... ave (Vs) = Qs / A = 3 m / s. A low-velocity zone can be observed near the inner side of the air intake wall of the air hood. Along the air intake surface of the air hood, from the low-velocity zone towards the center line of the air hood, a high-velocity zone can be observed where u > 3 m / s, and a high-velocity zone where u ≈ u. ave = 3 m / s region, and the central region where u is slightly < 3 m / s.

[0065] Figures 5-7Display the flow field of an opening hood with L / W = 1.54 and α = 150° on the front elevation (z = 0, parallel to the long side), the side elevation (x = 0, parallel to the short side), and the horizontal plane (y = 0, from the intake). The intake (length × width) = (L × W) = (1m × 0.65 m), with an area A = 0.65 m². 2 The outlet diameter D = 0.10 m, and the contraction section length E = 0.121 m. The intake volume Qs = 117 cm², the outlet velocity is 248 m / s, and the average intake velocity u... ave (Vs) = Qs / A = 3m / s. A low-velocity zone can be seen near the inner side of the air intake wall of the air hood. From the low-velocity zone towards the center of the air hood, the local velocity u gradually increases, forming a high-velocity zone approximately in the center. When the air intake size, outlet diameter, and intake volume remain constant, changing the contraction angle α results in a high-velocity central region and low-velocity surrounding areas, which is completely different from the velocity distribution at a small contraction angle α. The contraction section at a small contraction angle α is clearly more beneficial to the uniformity of the intake velocity distribution than the contraction section at a large contraction angle α. When L / W increases and approaches a trough shape, the flow pattern is similar to that at low L / W values, where... Figures 2-7 They share similar characteristics, and the value of the contraction angle α has a significant impact on the velocity distribution at the inlet.

[0066] Figures 8-10 The flow field at the intake on the horizontal plane is shown with L / W = 1.54 (Opening Hood), 6.06 (Slot Hood), and 10.00 (Slot Hood), varying the contraction angle α. Specifically, when L / W = 1.54 and y = 0 (intake), the average velocity u at the intake is... ave = 3 m / s. When L / W = 6.06 and y = 0 (inlet), the average velocity u at the inlet is... ave =11.818 m / s. When L / W = 10.00 and y = 0 (inlet), the average velocity u at the inlet is... ave = 19.500 m / s. The flow field pattern at the intake on the horizontal plane is quite complex and depends on the values ​​of L / W and α. However, regardless of whether the intake is rectangular or slotted, a high-speed zone will form in the center when α > 90°. When a high-speed zone forms in the center, the low-speed zone of the Opening Hood (L / W ≤ 5) surrounds the central high-speed zone, while the low-speed zone of the Slot Hood (L / W > 5) appears on both sides of the long side of the intake.

[0067] Figure 11 , Figure 12This displays the flow fields on the front and side facades near the low-velocity region of the Opening Hood (L / W = 1.54) at contraction angles of α = 30° and 150° (z = 0, x = 0). Among them... Figure 11 As shown, at α = 30°, a reflux bubble appears in the low-velocity zone inside the inlet edge; as Figure 11 As shown, at α = 150°, an "openbifurcation line" is presented, and the fluid on both sides of this line leaves the line. This is due to the enhanced three-dimensionality at large α angles.

[0068] Regarding aspect B. the distribution of velocity along the centerline, Figure 13 and Figure 14 The dimensionless velocity distribution along the centerline is shown for different contraction angles α, and all curves exhibit u / u ave The form of rapid decrease with y / Dh. When L / W≤5, the centerline velocity distribution will be similar to... Figure 13 Similar; when L / W > 5, the centerline velocity distribution will be similar to Figure 14 Similar, among them, Figure 14 part (a) and Figure 14 The curves in part (b) are almost identical when α ≤ 90°. The airflow characteristics of the two types of air hoods, Opening Hood and Slot Hood, are quite different.

[0069] From the basic theory, we know that the velocity u / u of the centerline of the circular or rectangular intake port of the opening hood is... ave The relationship with distance y / Dh is u / u ave ∝ (y / Dh)-2; The velocity u / u of the centerline of the slot-shaped intake of the Slot Hood. ave The relationship with distance y / Dh is u / u ave ∝ (y / Dh)-1. Therefore, the velocity u / u along the centerline of the circular or rectangular intake port is... ave The velocity decreases very rapidly as the distance y / Dh increases; the velocity u / u at the centerline of the slot-shaped intake port... ave As the distance y / Dh increases, the descent will be slower than that of circular or rectangular intake ports. Figure 13 and Figure 14 It also shows: Figure 13 The velocity u / u of the centerline of the Opening Hood in part (a) ave The ratio that decreases with increasing distance y / Dh Figure 14 Slot hood is fast. When y / Dh > 1.2, Figure 13 u / u in part (a) of the Opening Hood aveIt's already close to zero, but... Figure 14 In the slot hoods of parts (a) and (b), when y / Dh > 2, u / u ave It has not yet dropped to zero. The semi-empirical formula [Equation 1] of Dalla-Valle (1945) without inlet area correction and [Equation 2] of (1952) with inlet area correction are compared with... Figure 13 (b) The curves are plotted together on Figure 13 Comparing (b), it can be seen that: [Equation 1] without inlet area correction is quite close to the curve of α = 90° when y / Dh > 0.1; the center linear velocity predicted by [Equation 2] with inlet area correction is slightly higher than the curve of α = 90° when y / Dh > 0.1. The center linear velocities predicted by both equations are significantly different from the curve of α ≠ 90° when y / Dh < 0.5.

[0070] [Equation 1]

[0071] Dalla-Valle's semi-empirical formula (1945), without considering the correction for the inlet area A, is V(y) ∝ y. -2 :

[0072]

[0073] [Equation 2]

[0074] A correction was made considering the intake port area A (1952). 1 [ 1 Dalla Valle, JM, Exhaust Hoods. Industrial Press, 2nd ed., New York, 1952.], y ≤ 1.7 A 0.5 It can only be used when:

[0075]

[0076] V s : Surface velocity at the air intake of the air hood (inhalation volume / intake area)

[0077] V: The airflow velocity upstream of the center point y of the air intake on the center line of the air hood.

[0078] y: Distance upstream from the center point of the air intake of the air hood along the centerline.

[0079] D h Hydraulic diameter (also known as equivalent diameter ≡ 4A / p) e A is the cross-sectional area of ​​the intake port, p e (This refers to the circumference of the air intake)

[0080] observe Figure 13 Opening Hood and Figure 14 Regarding the Slot Hood, it can be noted that: (1). When α < 90°, the u / u of all L / W at the center point of the air hood intake (y / Dh = 0) ave < 1 (slightly less than 1). (2) When α = 90°, the u / u of all L / W at the center point of the air intake of the air hood (y / Dh = 0) ave ≈ 1 (slightly greater than 1). That is, when α = 90°, the velocity u at the center of the intake port is approximately equal to the average velocity u of the intake surface of the air hood. ave = Qs / A. When α > 90°, due to [ Figure 8 ]~[ Figure 10 The central high-speed zone is visible at the center point of the air intake of the air hood (y / Dh = 0) u / u ave > 1; The larger α is, the greater the u / u at y / Dh = 0. ave The larger. For example: ([ Figure 13 In the Opening Hood, when L / W = 1.54 and α = 150°, the value reaches as high as u / u at y / Dh = 0. ave ≈5.5; [ Figure 14 In the Slot Hood, L / W = 6.06 and 10.00 at α = 150° are approximately u / u at y / Dh = 0, respectively. ave ≈ 2.6 and 2.3).

[0081] Regarding C. the lateral distribution of velocity, Figure 15 , Figure 16 Display the dimensionless velocity u / u of an opening hood with L / W = 1.54 at y / Dh = 0.10 and 0.50 respectively. ave Laterally distributed, with contraction angles α = 30°, 60°, 90°, 120°, 150°. It can be observed that: (1). Figure 15 In part (a) (y / Dh = 0.10), when α > 90°, the dimensionless velocity magnitude u / u in the central region is... ave The velocity is much larger than that when α ≤ 90°. When α > 90°, the dimensionless velocity magnitude u / u ave In a transverse distribution parallel to the long side (x / L), the velocity decreases rapidly from the central region to both sides. Within the range of approximately [-(0.35~0.40)≤x / L≤+(0.35~0.40)], velocities with α > 90° are greater than those with α ≤ 90°. The magnitude of the dimensionless velocity u / u for α > 90° is given.ave The velocity decreases to almost the same as the velocity at α≤90° when x / L ≈ -(0.35 ~ 0.40) and +(0.35 ~ 0.40). The velocity u / u is the same when x / L < -(0.35 ~ 0.40) and > +(0.35 ~ 0.40), and α > 90°. ave Slightly smaller than the speed α≤90°. (2). Figure 15 In part (b) (y / Dh = 0.10), when α > 90°, the dimensionless velocity magnitude u / u ave The lateral distribution parallel to the shorter side (z / W) is greater than u / u for all z / W values ​​where α ≤ 90°. ave The magnitudes of the velocities u / u at small contraction angles α = 30° and 60°. ave The difference is not significant, and the value remains approximately the same within the range of [-0.40 ≤ z / W ≤ +0.40]. When z / W < -0.40 and > +0.40, u / u ave The speed gradually decreases. (3) Figure 16 (y / Dh = 0.50), α > u / u of 90゜ ave The magnitude of dimensionless velocity gradually evolves into a ratio Figure 15 The value is small, but still maintains a bell-shaped distribution. u / u ≤ 90° ave The dimensionless velocity magnitude gradually decreases, becomes similar in value, and evolves into a bell-shaped distribution. (4). For traditional canopy hoods and open hoods, if a more uniform inlet velocity is desired, α should be kept to ≤ 90°. (5). For canopy hoods and open hoods, u / u with α > 90°. ave The magnitude of the dimensionless velocity in the central region of [-(0.35 ~ 0.40)≤x / L≤+(0.35 ~ 0.40)] and [-0.40≤z / W≤+0.40] is significantly larger than that in the region of α≤90°. This phenomenon can still be observed up to y / Dh = 0.6 ~ 0.8. Therefore, to reduce the inhalation volume Qs, the contraction angle α of the opening hood can be made > 90°, and the contaminant source can be placed in the central region of [-(0.35 ~ 0.40)≤x / L≤+(0.35 ~ 0.40)] and [-0.40≤z / W≤+0.40], while keeping y / Dh < 0.6 (the closer to the inhalation port, the better).

[0082] Figures 17-20 Display the dimensionless velocities u / u for the slot hoods with L / W = 6.06 and 10.00 at y / Dh = 0.10 and 0.50, respectively. aveLaterally distributed, with contraction angles α = 30°, 60°, 90°, 120°, 150°. It can be observed that: (1). Figure 17 In part (a) (y / Dh = 0.10), when α > 60°, the dimensionless velocity magnitude u / u in the central region is... ave The velocity is much larger than that when α ≤ 60°. When α > 60°, the dimensionless velocity magnitude u / u ave In a transverse distribution parallel to the long side (x / L), the velocity decreases rapidly from the central region to both sides. Within the range of approximately [-(0.20 ~ 0.25) ≤ x / L ≤ +(0.20 ~ 0.25)], velocities with α > 60° are greater than those with α ≤ 60°. The magnitude of the dimensionless velocity u / u for α > 60° is given. ave The velocity decreases to almost the same as the velocity at α≤60° when x / L ≈ -(0.20~0.25) and +(0.20~0.25). When x / L < -(0.20~0.25) and > +(0.20~0.25), the velocity u / u > 60° is... ave It is much smaller than the speed of α≤60°. (2). Figure 17 In part (b) (y / Dh = 0.10), when α > 60°, the dimensionless velocity magnitude u / u ave The lateral distribution parallel to the short side (z / W) is greater than u / u for all z / W values ​​over the entire range of z / W, where α ≤ 60°. ave The magnitudes of the velocities u / u at small contraction angles α = 30° and 60°. ave The difference is not significant, and the value remains approximately the same within the range of [-0.40 ≤ z / W ≤ +0.40]. When z / W < -0.40 and > +0.40, u / u ave The speed gradually decreased, but the magnitude was not significant. (3) Figure 18 Part (a) (y / Dh = 0.50) and Figure 17 The u / u of part (a) (y / Dh = 0.10) ave The dimensionless velocity distribution patterns are similar: α > 60° is bell-shaped, while α ≤ 60° is flatter, but the value at the middle x / L = 0 drops significantly. Figure 18 The u / u of part (b) (y / Dh = 0.50) ave The magnitude of dimensionless velocity gradually evolves into a ratio Figure 17 The (b) part is small and gradually evolves into a slightly raised bell shape. (4). The dimensionless velocity magnitude u / u of the Slot Hood aveThe lateral distribution of y / Dh varies more slowly with distance from the intake port than that of the Opening Hood. (5) For a more uniform intake port velocity in a traditional Slot Hood, α ≤ 60°. (6) For a Slot Hood, α > 60° for u / u ave The magnitude of the dimensionless velocity in the central region of [-(0.20 ~ 0.25)≤x / L≤+(0.20 ~ 0.25)] is significantly larger than that in the region of α≤60°, and this phenomenon can still be observed up to y / Dh = 1.0 ~ 1.2. Therefore, to reduce the inspiratory volume Qs, the contraction angle α of the SlotHood can be made > 60°, and the contaminant source can be placed in the central region of [-(0.20 ~ 0.25)≤x / L≤+(0.20 ~ 0.25)], [-0.40≤z / W≤+0.40], and y / Dh < 1.0, the closer to the inspiratory port the better.

[0083] Regarding D. the variation of the lateral velocity distribution nonuniformity η with α (with fixed L / W):

[0084] The velocity distribution "non-uniformity" η is defined as follows:

[0085]

[0086] Where: u i u represents the local airflow velocity magnitude. ave N represents the average airflow velocity, and N is the number of points used for averaging.

[0087] Figure 21 Display multiple dimensionless velocities u / u on a plane of symmetry parallel to the long side when the opening hood contraction angle α changes with L / W = 1.54 and the contraction angle α changes. ave Lateral nonuniformity. The nonuniformity η of all y / Dh increases with increasing contraction angle α. When α > 90°, the rate of increase of nonuniformity η with increasing contraction angle α is much greater than the rate of increase when α ≤ 90°. Therefore, Opening Hood aims to maintain a small dimensionless velocity u / u ave The lateral non-uniformity needs to be such that α ≤ 90°. Figure 22 and Figure 23 The dimensions of multiple dimensionless velocities u / u in y / Dh are as the contraction angle α changes for L / W = 6.06 and L / W = 10.00, respectively. aveThe non-uniformity of the lateral distribution. The non-uniformity η of all y / Dh increases with increasing contraction angle α. When α > 60°, the rate of increase of non-uniformity η with increasing contraction angle α is much greater than the rate of increase when α ≤ 60°. Therefore, the Slot Hood aims to maintain a small dimensionless velocity u / u ave The lateral distribution non-uniformity must be such that α ≤ 60°.

[0088] Regarding the variation of E. the lateral non-uniformity of velocity distribution η with α (with y / Dh fixed): Figure 24 part (a) and Figure 24 Part (b) shows the dimensionless velocities u / u on the planes of symmetry parallel to the long side and parallel to the short side, respectively, when the opening hood and slot hood contraction angle α changes at y / Dh = 0.10. ave Variation of lateral distribution non-uniformity η. Figure 24 In part (a), the lateral non-uniformity η of the plane of symmetry parallel to the long side of the Opening Hood and the Slot Hood increases with the increase of the contraction angle α; the η of the Slot Hood is much larger than that of the Opening Hood, and the rate of increase with the increase of α is also higher than that of the Opening Hood. Figure 24 In part (b), the lateral non-uniformity η of the symmetry plane parallel to the short side of the Opening Hood increases with the increase of the contraction angle α, but the non-uniformity η of the Slot Hood remains at a low value with almost no change. The lateral non-uniformity η of the symmetry plane parallel to the short side of the Opening Hood is much larger than that of the Slot Hood.

[0089] The design steps for an opening hood (L / W≤5) are as follows:

[0090] 1. When using an Opening Hood, the required airflow volume is much greater than that described below for Slot Hood and Multiple Slot Hood designs. If a smaller airflow volume is desired to achieve a larger and more uniform inlet velocity, the preferred choice is to use the Slot Hood and Multiple Slot Hood discussed below.

[0091] 2. If there are concerns about interference from environmental airflow, the interfering airflow should be blocked.

[0092] 3. Use [ Figure 51 The ACGIH Manual formula is used to calculate the required inspiratory volume [Qs = V (10Y2 + A)] and inspiratory rate [Vs = V [(10Y2 / A) + 1].

[0093] 4. Suction Port Configuration: When the air hood is equipped with suction ports to connect to the suction pipe, the relative position between the suction port and the air hood's suction surface affects the "non-uniformity" η of the spatial distribution of the suction velocity at the air hood's suction port. If the suction velocity "non-uniformity" is too high, the efficiency of the air hood in drawing contaminants into the suction channel will decrease. Therefore, the placement of the suction ports must be carefully considered to avoid reducing the air hood's efficiency in removing contaminants. Designers should evaluate, calculate, and select a suitable suction port configuration method using the following methods.

[0094] (1) The air intake is located on the top and side of the air hood cavity: the air intake port is not connected to the pipe fan for air intake on the top and side of the cavity, so as to avoid the air intake speed of the air intake groove being too uneven in the horizontal direction.

[0095] (2). The air intake hole is located behind the air inlet:

[0096] <1> A tapered nozzle can be used, but the taper angle (full angle) α should be ≤0º to avoid excessive unevenness in the lateral distribution of the suction velocity in the suction groove.

[0097] <2> To prevent excessive inhalation, you can:

[0098] (a). The contraction angle (full angle) of the tapering segment α > 90° (e.g., 120° or 150°).

[0099] (b) Try to place the source of pollutants within the central area of ​​[-(0.35~0.40)≤x / L≤+(0.35~0.40)] and [-0.40≤z / W≤+0.40].

[0100] (c) Try to make [y / Dh < 0.6] (the smaller y / Dh is, the closer the pollutant source is to the inlet).

[0101] For the symbols [(x, y, z), L, W], please refer to [the above symbols]. Figure 1 When using this method, because the velocity of the air shield in the central region is greater than the average velocity, the contraction angle α of the convergence section is larger, and the velocity u / u in the central region is also greater. ave The larger (see Figures 15-20 Therefore, a smaller intake volume can be used to reach the desired speed at the pollutant source. In addition, because the pollutant emission source is quite close to the air hood intake when using this method, for ease of operation, it may be necessary to use an air hood or pollutant source lifting mechanism, combined with a two-stage intake volume (high and low).

[0102] Design of a slot hood (L / W > 5):

[0103] Method A:

[0104] 1. If there are considerations regarding environmental airflow interference, the interfering airflow should be blocked.

[0105] 2. Use [ Figure 51 The ACGIH Manual formula calculates the required inspiratory volume Qs = 3.7LVY and inspiratory velocity Vs = 3.7VY / W.

[0106] 3. Suction port configuration (Method A): The suction port is located behind the suction groove:

[0107] (1) Use a tapered pipe, but the taper angle (full angle) α should be ≤60º to avoid excessive unevenness η in the lateral distribution of the suction velocity in the suction groove. However, if the taper angle α≤60º, the taper section may sometimes be too long, which is not conducive to actual installation. In this case, α≤90º is acceptable.

[0108] (2) To prevent excessive inhalation, you can:

[0109] (a) The contraction angle (full angle) of the tapering segment α > 90° (e.g., 120° or 150°).

[0110] (b) Try to place the source of pollutants within the central area of ​​[-(0.20 ~ 0.25)≤x / L≤+(0.20 ~ 0.25)].

[0111] (c) Make [y / Dh < 1.0] (the smaller the y / Dh, the closer the pollutant source is to the inlet).

[0112] For the symbols [(x, y, z), L, W], please refer to [the above symbols]. Figure 1 When using this method, because the velocity of the air shield in the central region is greater than the average velocity, the contraction angle α of the convergence section is larger, and the velocity u / u in the central region is also greater. ave The larger (see Figures 15-20 Therefore, a smaller intake volume can be used to reach the desired speed at the pollutant source. In addition, because the pollutant emission source is quite close to the air hood intake when using this method, for ease of operation, it may be necessary to use an air hood or pollutant source lifting mechanism, combined with a two-stage intake volume (high and low).

[0113] Method B:

[0114] 1. If there is no environmental airflow interference and no curtains or sidewalls are installed, and if you want to prevent the air intake velocity from being too high, you can place the pollutant release port at Y / Dh < 2.0.

[0115] 2. If there are considerations regarding environmental airflow interference, the interfering airflow should be blocked.

[0116] 3. Use [Table 1] to design the required inhalation speed.

[0117] 4. Geometric Design: If the velocity distribution in the suction groove is sufficiently uniform, then

[0118] (1) Groove length L:

[0119] If there is a risk of lateral dispersion of pollutants, the length of the air intake of the air hood should be adjusted.

[0120] L≥1.5 × [Pollution source emission width]

[0121] If there is no risk of lateral dispersion of pollutants, the length of the air intake of the air hood should be adjusted.

[0122] L = [Pollution source emission width]

[0123] (2) Channel width Ws: 1.5 cm≤W = Ws≤2 cm, to avoid excessive pressure loss and flow rate.

[0124] 5. Suction port configuration: The suction port is located behind the suction slot, taking into account... Figure 25 The Slot Hood design parameters show the tapered nozzle when Hhood ≥ 5 cm (δb = 1 cm) and 1.5 cm ≤ W = Ws ≤ 2 cm. The lateral non-uniformity of the intake velocity distribution increases with the contraction angle α. When the contraction angle (full angle) α of the tapered section ≤ 60º, a very small lateral non-uniformity of the intake velocity distribution in the intake slot can be obtained. Even if the contraction angle α = 90º of the tapered section, the non-uniformity of the intake velocity in the intake slot is still only 12.5%, so α ≤ 90º can also be used in the design. If α > 90º and the contaminant source is very close to the intake slot, the maximum length of the contaminant source should be within ±0.30L of the centerline of the hood.

[0125] 6. The design principle in point 5 above is based on Figure 26 and Figure 27 The flow field analysis results.

[0126] Method C:

[0127] 1. If there are considerations regarding environmental airflow interference, the interfering airflow should be blocked.

[0128] 2. Use [Table 1] to design the required inhalation speed.

[0129] 3. Geometric Design: If the velocity distribution in the suction slot is sufficiently uniform, then

[0130] (1) Slot length L: If the velocity distribution in the suction slot is sufficiently uniform, then

[0131] If there is a risk of lateral dispersion of pollutants, the length of the air intake of the air hood should be adjusted.

[0132] L≥1.5 × [Pollution source emission width]

[0133] If there is no risk of lateral dispersion of pollutants, the length of the air intake of the air hood should be adjusted.

[0134] L = [Pollution source emission width]

[0135] (2) Channel width Ws: 1.5 cm≤W = Ws≤2 cm, to avoid excessive pressure loss and flow rate.

[0136] 4. Air intake port configuration (method C1): The air intake port is located on the upper plate of the air hood cavity, and the air intake groove is located on the lower side of the air hood cavity, such as... Figure 28 The design parameters of the Slot Hood. A Slot Hood with an air intake port located above the air hood cavity. The distance S between the leading edge of the air intake port and the air intake surface of the air hood must be large enough to ensure that the "non-uniformity" η of the air intake speed in the air intake slot is low in the lateral direction. Figures 29-32 This shows the minimum critical distance Scri between the leading edge of the intake port and the intake surface of the air hood, required to achieve a slot hood intake velocity with a lateral non-uniformity (η) of less than 10%. As can be seen from the figure:

[0137] (1) When Hhood and D are fixed, Scri increases rapidly with the increase of L.

[0138] (2) When L and D are fixed, Scri decreases as Hhood increases.

[0139] Air intake port configuration (method C2): The air intake port is located on the upper plate of the air hood cavity, and the air intake groove is located on one side of the lower plate of the air hood cavity, such as... Figure 33 The design parameters for the Slot Hood are as follows. The distance S between the leading edge of the intake port and the side of the hood must be large enough to ensure that the lateral "non-uniformity" η of the intake velocity in the intake slot is sufficiently low. Figure 34 , Figure 35 Display: The minimum critical distance Scri between the leading edge of the intake port and the side of the air hood is required to make the intake speed of the slot hood less than 10% when the non-uniformity (η) of the transverse distribution is less than 10%.

[0140] Air intake port configuration (method C3): The air intake port is located on the upper plate of the air hood cavity, and the air intake groove is located in the center of the lower plate of the air hood cavity, such as... Figure 36 The design parameters of the Slot Hood. The distance between the air intake and the lower plate of the hood must be large enough to ensure that the lateral "non-uniformity" η of the air intake velocity in the air intake slot is sufficiently low. Figure 37 , Figure 38 Display: The minimum critical distance Hcri between the air intake and the lower plate of the air hood is required to make the intake speed of the Slot Hood less than 10% when the non-uniformity (η) of the transverse distribution is less than 10%.

[0141] Design procedure for Slot Hood (aspect ratio L / W > 5):

[0142] 1. Suction groove length L: If there is a risk of lateral dispersion of pollutants, the suction groove length L should be ≥ 1.5 × [pollutant source dispersion width]; if there is no risk of lateral dispersion of pollutants, the suction groove length L should be ≈ [pollutant source dispersion width].

[0143] 2. Inhalation groove width Ws: The width of the inhalation groove can be selected as 1.5≤Ws≤2 cm to avoid pressure loss or excessive air intake.

[0144] 3. Methods C1 and C2: Based on the designed Hhood, in Figures 29-32 or Figures 34-35 Choose the appropriate diagram from the available options, and then select Scri based on the L and D dimensions of the design.

[0145] Method C3: Based on the design S, in Figures 37-38 Choose the appropriate diagram from the available options; then select HCRI based on the L and D dimensions of the design.

[0146] 4. To avoid the air hood depth Dhood being too large, consider installing an air intake port every 120-140 cm of air hood length.

[0147] 5. Use [Table 1] to design the required inhalation speed.

[0148] Design of Multiple-Slot Hood

[0149] Method A:

[0150] 1. If there are considerations regarding environmental airflow interference, the interfering airflow should be blocked.

[0151] 2. Use [Table 1] to design the required inhalation speed.

[0152] 3. Geometric Design: If the velocity distribution in the suction slot is sufficiently uniform, then

[0153] (1) Height W: should cover the maximum height at which pollutants rise.

[0154] (2) Slot length L: If the suction slot velocity is sufficiently uniform, then

[0155] If there is a risk of pollutants spreading laterally,

[0156] The length of the air intake channel L is greater than or equal to 1.5 × [the width of the pollution source].

[0157] If there is no risk of lateral dispersion of pollutants,

[0158] The length of the air intake channel, L, is approximately equal to the width of the pollution source.

[0159] (3) Groove width Ws: 1.5≤Ws≤2 cm can be selected to avoid pressure loss or excessive air intake.

[0160] (4) Spacing between adjacent air intake slots Wc: Wc / Ws = 5 ~ 7 (maximum not exceeding 9).

[0161] 4. Suction port configuration: The suction port is located at the rear of the air hood cavity (Method A), considering... Figure 39 Design parameters for when the air intake is located at the rear of the air hood cavity. If the air intake is located on the rear plate of the air hood cavity, a sufficiently long tapered section should be connected between the air intake and the air intake pipe, and the taper angle (full angle) α of the tapered section should be ≤60º to avoid excessively uneven distribution of the air intake velocity in the lateral and longitudinal directions. Even when the taper angle α = 90º, the unevenness of the air intake velocity in the air intake is still ≤10%, so α≤90º can also be used in the design. If α > 60º, during use, the source of contaminants should be as close as possible to the air intake of the air hood; and the maximum length of the source of contaminants should be within ±0.30L of the centerline of the air hood.

[0162] 5. The design principle in point 4 above is based on Figure 40 and Figure 41 The flow field analysis results.

[0163] Method B:

[0164] 1. If there are considerations regarding environmental airflow interference, the interfering airflow should be blocked.

[0165] 2. Use [Table 1] to design the required inhalation speed.

[0166] 3. Geometric Design: If the velocity distribution in the suction groove is sufficiently uniform, then as shown in […]. Figure 42 As shown:

[0167] (1) Height W: should cover the maximum height at which pollutants rise.

[0168] (2) Slot length L: If the suction slot velocity is sufficiently uniform, then

[0169] If there is a risk of pollutants spreading laterally,

[0170] The length of the air intake channel L is greater than or equal to 1.5 × [the width of the pollution source].

[0171] If there is no risk of lateral dispersion of pollutants,

[0172] The length of the air intake channel, L, is approximately equal to the width of the pollution source.

[0173] (3) Groove width Ws: 1.5≤Ws≤2 cm can be selected to avoid pressure loss or excessive air intake.

[0174] (4) Spacing between adjacent air intake slots Wc: Wc / Ws = 5 ~ 7 (maximum not exceeding 9).

[0175] 4. Suction port configuration: The suction port is located on the upper plate of the air hood cavity, taking into consideration... Figure 43 The design parameters for the Multiple-Slot Hood are as follows: The "lateral non-uniformity" of the suction velocity in the uppermost suction slot will be greater than that in the lower suction slots; the "longitudinal non-uniformity" of the suction velocity in each suction slot will be greater along the central vertical line of the suction surface of the air hood than further away from the central vertical line. For a Multiple-Slot Hood with a suction port located above the air hood cavity, the distance S between the leading edge of the suction port and the suction surface of the air hood must be sufficiently large to ensure that the lateral "non-uniformity" η and the longitudinal "non-uniformity" ζ of the suction velocity in the suction slots are sufficiently low. Figure 43 The symbols are explained below:

[0176] The diameter of the intake port above the air hood cavity is D≥10 cm.

[0177] Dhood Inner Depth of Air Shield Cavity

[0178] Hhood inner height

[0179] L is the length of the air intake groove, L≤200 cm

[0180] Lhood inner side length of the air mask cavity

[0181] S is the distance from the leading edge of the air intake port above the air mask cavity to the inner side of the air intake surface of the air mask cavity.

[0182] Scri is S such that η≤10% and ζ≤10%.

[0183] t air cover thickness

[0184] The distance from the upper edge of the top air intake slot to the lower edge of the bottom air intake slot (W)

[0185] Ws Intake slot width

[0186] Wc is the distance between the center lines of two adjacent intake slots.

[0187] A rectangular coordinate system of x, y, z, with the origin located at the lower left corner of the inner side of the air hood cavity.

[0188] δs is the shortest distance from the short side of the intake groove to the nearest point in the air hood cavity, ≥1 cm.

[0189] δtb is the shortest distance from the long side of the intake groove to the air hood cavity, ≥1 cm.

[0190] ξ is the horizontal coordinate along the center line of the uppermost air intake groove, with the origin at the left end of the air intake groove.

[0191] η is the non-uniformity of the inlet velocity distribution of the uppermost suction slot in the lateral (x direction) direction (= )

[0192] The non-uniformity of the inlet velocity distribution of each suction slot in the longitudinal (y-direction) at ξ = L / 2.

[0193] For example: Figure 44 The diagram shows a Multiple-Slot Hood with W = 31.5 cm. The diameter of the intake hole at the top of the hood is D = 15 cm. The lengths of the intake slots are L = 4D, 6D, 8D, and 10D, the width is Ws = 1.5 cm, the gap between adjacent intake slots is Wc = 5Ws = 7.5 cm, and δs = δtb = 1 cm. If u is the local wind speed perpendicular to the intake surface on the center line of the uppermost intake slot, u ave Let U be the average velocity perpendicular to the centerline of the suction surface on the centerline of the uppermost suction slot. Then, when the distance S between the leading edge of the suction port and the suction surface of the air hood is designed to be too small (0.01 m), the dimensionless local inlet velocity u / u of the uppermost suction slot will be... ave Along the dimensionless lateral distance ξ / L, the distribution has a large value in the central region, and a smaller value on both sides u / u. ave The difference becomes very small, so the "lateral non-uniformity" η of the suction velocity in the suction slot is large; if S is designed to be large enough (> 0.10 m), then the dimensionless local inlet velocity u / u in the uppermost suction slot will be large. ave Along the dimensionless lateral distance ξ / L, the difference between the central region and the sides is small, so the "lateral non-uniformity" η of the suction velocity in the suction slot is relatively small. The larger S is, the smaller the "lateral non-uniformity" η will be, and the same applies to the "longitudinal non-uniformity" ζ. If the suction port of the connecting circular tube is set on the upper plate of the air hood, the distance S between the leading edge of the suction port and the suction surface of the air hood must be large enough to ensure that the lateral and longitudinal non-uniformities η and ζ of the suction velocity in each suction slot are sufficiently small.

[0194] 5. The design principles for the air intake vent position mentioned above are based on... Figures 45-50 The analysis results.

[0195] Among them Figures 45-50 The display shows the minimum critical distance Scri between the leading edge of the suction port and the suction surface, designed to ensure that the non-uniformity (η and ζ) of the suction velocity distribution in the Multiple-Slot Hood is less than 10% in both the lateral and longitudinal directions.

[0196] Ws = 1.5 ~ 2.0 cm, Wc / Ws = 5 ~ 7 (maximum not exceeding 9),

[0197] δtb = δs = 1 cm

[0198] L≤200 cm

[0199] 10≤D≤20 cm

[0200] Vs≤20 m / s (Vs = Qs / A)

[0201] η < 10%, ζ < 10%

[0202] As can be seen from the figure:

[0203] (1) When W and D are fixed, Scri increases rapidly as L increases.

[0204] (2) When L and D are fixed, Scri increases as W increases.

[0205] Design procedure for Multiple-Slot Hood Method B:

[0206] 1. Suction groove length L: If there is a risk of lateral dispersion of pollutants, the suction groove length L should be ≥ 1.5 × [pollutant source dispersion width]; if there is no risk of lateral dispersion of pollutants, the suction groove length L should be ≈ [pollutant source dispersion width].

[0207] 2. Inhalation groove width Ws: The width of the inhalation groove can be selected as 1.5≤Ws≤2 cm to avoid pressure loss or excessive air intake.

[0208] 3. Spacing between adjacent suction slots Wc: The ratio of the center-line spacing Wc between two adjacent suction slots to the width Ws of the suction slot, Wc / Ws, is ≤5 ~ 7, and the maximum shall not exceed 9.

[0209] 4. Design W, L, D:

[0210] (1) According to W, in Figures 29-34 Choose the appropriate graph for use (each graph has a suggested range of W values).

[0211] (2) Based on the values ​​of L and D, find the corresponding Scri value. Choose an S such that S≥Scri.

[0212] 5. To avoid the air hood depth Dhood being too large, consider installing an air intake port every 120-140 cm of air hood length.

[0213] 6. Use [Table 1] to design the required inhalation speed.

[0214] In summary, based on the content disclosed above, the present invention can indeed achieve the intended purpose, providing a method for using and configuring air hoods that, through empirical results conforming to gas dynamics, employ air hood types with different contraction angles, can not only effectively remove gaseous pollutants from pollution sources near the intake port, but also reduce power consumption to save energy and carbon emissions, thus having great industrial application value.

[0215] Table 1: Empirical values ​​of minimum inspiratory rate used for Multiple-Slot Hood [Method A, B] and Slot Hood [Method B, C]

[0216]

[0217] Note:

[0218] <1> Y*: Distance from the air intake to the farthest point of the pollutant source.

[0219] <2> Vup: The speed at which pollutants are emitted upwards from the point of origin.

[0220] <3> Vs, min: The minimum required suction speed for the intake port when using a Multiple-Slot Hood or Slot Hood (Opening Hood is also acceptable) for "rear suction" or "side suction," suitable for use with organic solvents. If the contaminant is dust, Vs, min needs to be increased as needed.

[0221] <4> For liquid chemicals in a general chemical tank, if the temperature does not exceed approximately 50-60°C, then using the gas hood configuration method C, Vup ≈ 0.2 m / s to estimate the required Vs, min is generally sufficient.

[0222] <5> For tasks involving high-temperature cooking, the distance Y* should be minimized. For example, if Y* = 0.3 m, Vs,min should be ≥ 13 m / s; if Y* = 0.5 m, Vs,min should be ≥ 20 m / s. Furthermore, there should be appropriate measures to partially cover the surrounding area.

Claims

1. A method for configuring and using an air hood, characterized in that, The air hood has an intake port, a converging section, and an outlet. The intake port has a length of L and a width of W. The intake port is connected to the front end of the converging section, which is a rectangular pyramid that tapers from front to back. The long side of the converging section has a contraction angle. The outlet is connected to the rear end of the converging section. The outlet is connected to a pipe, which in turn is connected to a fan. When a pollution source at the front end of the intake port emits gaseous pollutants, the gaseous pollutants are drawn in through the intake port and then discharged outwards through the outlet. The method of using and configuring the air hood includes the following steps: A: Confirm the extent of the gaseous pollutants emitted from this pollution source; and B: Select the angle of the contraction angle; Step A involves confirming the width of the gaseous pollutants emitted from the pollution source, which corresponds to the long side of the contraction section. Wherein (a) when using an open-type air hood with L / W ≤ 5: (i) If the gaseous pollutants in step A are widely dispersed and a more uniform inlet velocity is required, then in step B, the angle of the contraction angle should be ≤90°. (ii) If the range of gaseous pollutants emitted in step A is concentrated and it is necessary to reduce the intake volume, then in step B, the angle of contraction should be greater than 90°. Or (b) when using a single-slot air hood with L / W > 5: (i) If the gaseous pollutants in step A are widely dispersed and a more uniform intake velocity is required, then in step B, the angle of contraction ≤ 60° should be selected. (ii) If the range of gaseous pollutants emitted in step A is concentrated and it is necessary to reduce the intake volume, then in step B, the angle of contraction angle is selected to be > 60°.

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